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Sasvari Z, Alatriste Gonzalez P, Nagy PD. Tombusvirus-yeast interactions identify conserved cell-intrinsic viral restriction factors. FRONTIERS IN PLANT SCIENCE 2014; 5:383. [PMID: 25157258 PMCID: PMC4127529 DOI: 10.3389/fpls.2014.00383] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2014] [Accepted: 07/18/2014] [Indexed: 05/23/2023]
Abstract
To combat viral infections, plants possess innate and adaptive immune pathways, such as RNA silencing, R gene and recessive gene-mediated resistance mechanisms. However, it is likely that additional cell-intrinsic restriction factors (CIRF) are also involved in limiting plant virus replication. This review discusses novel CIRFs with antiviral functions, many of them RNA-binding proteins or affecting the RNA binding activities of viral replication proteins. The CIRFs against tombusviruses have been identified in yeast (Saccharomyces cerevisiae), which is developed as an advanced model organism. Grouping of the identified CIRFs based on their known cellular functions and subcellular localization in yeast reveals that TBSV replication is limited by a wide variety of host gene functions. Yeast proteins with the highest connectivity in the network map include the well-characterized Xrn1p 5'-3' exoribonuclease, Act1p actin protein and Cse4p centromere protein. The protein network map also reveals an important interplay between the pro-viral Hsp70 cellular chaperone and the antiviral co-chaperones, and possibly key roles for the ribosomal or ribosome-associated factors. We discuss the antiviral functions of selected CIRFs, such as the RNA binding nucleolin, ribonucleases, WW-domain proteins, single- and multi-domain cyclophilins, TPR-domain co-chaperones and cellular ion pumps. These restriction factors frequently target the RNA-binding region in the viral replication proteins, thus interfering with the recruitment of the viral RNA for replication and the assembly of the membrane-bound viral replicase. Although many of the characterized CIRFs act directly against TBSV, we propose that the TPR-domain co-chaperones function as "guardians" of the cellular Hsp70 chaperone system, which is subverted efficiently by TBSV for viral replicase assembly in the absence of the TPR-domain co-chaperones.
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Affiliation(s)
| | | | - Peter D. Nagy
- *Correspondence: Peter D. Nagy, Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, Lexington, KY 40546, USA e-mail:
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Nicholson BL, White KA. Functional long-range RNA-RNA interactions in positive-strand RNA viruses. Nat Rev Microbiol 2014; 12:493-504. [PMID: 24931042 PMCID: PMC7097572 DOI: 10.1038/nrmicro3288] [Citation(s) in RCA: 104] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Long-range RNA–RNA interactions, many of which span several thousands of nucleotides, have been discovered within the genomes of positive-strand RNA viruses. These interactions mediate fundamental viral processes, including translation, replication and transcription. In certain plant viruses that have uncapped, non-polyadenylated RNA genomes, translation initiation is facilitated by 3′ cap-independent translational enhancers (3′ CITEs) that are located in or near to their 3′ UTRs. These RNA elements function by binding to either the ribosome-recruiting eukaryotic translation initiation factor 4F (eIF4F) complex or ribosomal subunits, and they enhance translation initiation by engaging the 5′ end of the genome via a 5′-to-3′ RNA-based bridge. The activities of the internal ribosome entry sites (IRESs) in the 5′ UTRs of various viruses are modulated by RNA-based interactions between the IRESs and elements near to the 3′ ends of their genomes. In several plant viruses, translational recoding events, including ribosomal frameshifting and stop codon readthrough, have been found to rely on long-range RNA–RNA interactions. Multiple 5′-to-3′ base-pairing interactions facilitate genome circularization in flaviviruses, which has been proposed to reposition the 5′-bound RNA-dependent RNA polymerase (RdRp) to the initiation site of negative-strand synthesis at the 3′ terminus. The long-distance interaction between two cis-acting replication elements in tombusviruses generates a bipartite RNA platform for the assembly of the replicase complex and repositions the internally bound RdRp to the 3′ terminus. Tombusviruses also rely on several long-range interactions that mediate the premature termination of the RdRp during negative-strand synthesis that leads to transcription of subgenomic mRNAs (sgmRNAs). In a coronavirus, an exceptionally long-range interaction, which spans ∼26,000 nucleotides, promotes polymerase repriming during the discontinuous template synthesis step of sgmRNA-N transcription. A challenge for the future will be to determine how these long-range interactions are integrated and regulated in the complex context of viral RNA genomes.
Long-range intragenomic RNA–RNA interactions in the genomes of positive-strand RNA viruses involve direct nucleotide base pairing and can span distances of thousands of nucleotides. In this Review, Nicholson and White discuss recent insights into the structure and function of these genomic features and highlight their diverse roles in the gene expression and genome replication of positive-strand RNA viruses. Positive-strand RNA viruses are important human, animal and plant pathogens that are defined by their single-stranded positive-sense RNA genomes. In recent years, it has become increasingly evident that interactions that occur between distantly positioned RNA sequences within these genomes can mediate important viral activities. These long-range intragenomic RNA–RNA interactions involve direct nucleotide base pairing and can span distances of thousands of nucleotides. In this Review, we discuss recent insights into the structure and function of these intriguing genomic features and highlight their diverse roles in the gene expression and genome replication of positive-strand RNA viruses.
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Affiliation(s)
- Beth L Nicholson
- Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada
| | - K Andrew White
- Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada
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Qiu Y, Miao M, Wang Z, Liu Y, Yang J, Xia H, Li XF, Qin CF, Hu Y, Zhou X. The RNA binding of protein A from Wuhan nodavirus is mediated by mitochondrial membrane lipids. Virology 2014; 462-463:1-13. [PMID: 25092456 PMCID: PMC7112130 DOI: 10.1016/j.virol.2014.05.022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 04/06/2014] [Accepted: 05/21/2014] [Indexed: 01/19/2023]
Abstract
RNA replication of positive-strand (+)RNA viruses requires the lipids present in intracellular membranes, the sites of which viral replicases associate with. However, the direct effects of membrane lipids on viral replicases are still poorly understood. Wuhan nodavirus (WhNV) protein A, which associates with mitochondrial membranes, is the sole replicase required for RNA replication. Here, we report that WhNV protein A binds to RNA1 in a cooperative manner. Moreover, mitochondrial membrane lipids (MMLs) stimulated the RNA binding activity and cooperativity of protein A, and such stimulations exhibited strong selectivity for distinct phospholipids. Interestingly, MMLs stimulated the RNA-binding cooperativity only at higher protein A concentrations. Further investigation showed that MMLs stimulate the RNA binding of protein A by promoting its self-interaction. Finally, manipulating MML metabolism affected the protein A-induced RNA1 recruitment in cells. Together, our findings reveal the direct effects of membrane lipids on the RNA binding activity of a nodaviral replicase. WhNV protein A directly binds to RNA1 in a cooperative manner. Mitochondrial membrane lipids (MMLs) stimulate the binding activity of protein A. The RNA binding of protein A is selectively stimulated by specific phospholipids. MMLs enhance the RNA binding of protein A by stimulating its self-interaction. Manipulating phospholipid metabolism regulates protein A-induced RNA1 recruitment.
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Affiliation(s)
- Yang Qiu
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China; State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China
| | - Meng Miao
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Zhaowei Wang
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Yongxiang Liu
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Jie Yang
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Hongjie Xia
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Xiao-Feng Li
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China
| | - Cheng-Feng Qin
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China
| | - Yuanyang Hu
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Xi Zhou
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China.
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The hop-like stress-induced protein 1 cochaperone is a novel cell-intrinsic restriction factor for mitochondrial tombusvirus replication. J Virol 2014; 88:9361-78. [PMID: 24920799 DOI: 10.1128/jvi.00561-14] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
UNLABELLED Recent genome-wide screens reveal that the host cells express an arsenal of proteins that inhibit replication of plus-stranded RNA viruses by functioning as cell-intrinsic restriction factors of viral infections. One group of cell-intrinsic restriction factors against tombusviruses contains tetratricopeptide repeat (TPR) domains that directly interact with the viral replication proteins. In this paper, we find that the TPR domain-containing Hop-like stress-inducible protein 1 (Sti1p) cochaperone selectively inhibits the mitochondrial membrane-based replication of Carnation Italian ringspot tombusvirus (CIRV). In contrast, Sti1/Hop does not inhibit the peroxisome membrane-based replication of the closely related Tomato bushy stunt virus (TBSV) or Cucumber necrosis virus (CNV) in a yeast model or in plants. Deletion of STI1 in yeast leads to up to a 4-fold increase in CIRV replication, and knockdown of the orthologous Hop cochaperone in plants results in a 3-fold increase in CIRV accumulation. Overexpression of Sti1p derivatives in yeast reveals that the inhibitory function depends on the TPR1 domain known to interact with heat shock protein 70 (Hsp70), but not on the TPR2 domain interacting with Hsp90. In vitro CIRV replication studies based on isolated mitochondrial preparations and purified recombinant proteins has confirmed that Sti1p, similar to the TPR-containing Cyp40-like Cpr7p cyclophilin and the Ttc4 oncogene-like Cns1 cochaperone, is a strong inhibitor of CIRV replication. Sti1p interacts and colocalizes with the CIRV replication proteins in yeast. Our findings indicate that the TPR-containing Hop/Sti1 cochaperone could act as a cell-intrinsic virus restriction factor of the mitochondrial CIRV, but not against the peroxisomal tombusviruses in yeast and plants. IMPORTANCE The host cells express various cell-intrinsic restriction factors that inhibit the replication of plus-stranded RNA viruses. In this paper, the authors find that the Hop-like stress-inducible protein 1 (Sti1p) cochaperone selectively inhibits the mitochondrial membrane-based replication of Carnation Italian ringspot tombusvirus (CIRV) in yeast. Deletion of STI1 in yeast or knockdown of the orthologous Hop cochaperone in plants leads to increased CIRV replication. In addition, overexpression of Sti1p derivatives in yeast reveals that the inhibitory function depends on the TPR1 domain known to interact with heat shock protein 70 (Hsp70), but not on the TPR2 domain interacting with Hsp90. In vitro CIRV replication studies based on isolated mitochondrial preparations and purified recombinant proteins have confirmed that Sti1p is a strong inhibitor of CIRV replication. The authors' findings reveal that the Hop/Sti1 cochaperone could act as a cell-intrinsic restriction factor against the mitochondrial CIRV, but not against the related peroxisomal tombusviruses.
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Noncanonical role for the host Vps4 AAA+ ATPase ESCRT protein in the formation of Tomato bushy stunt virus replicase. PLoS Pathog 2014; 10:e1004087. [PMID: 24763736 PMCID: PMC3999190 DOI: 10.1371/journal.ppat.1004087] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2014] [Accepted: 03/07/2014] [Indexed: 12/13/2022] Open
Abstract
Assembling of the membrane-bound viral replicase complexes (VRCs) consisting of viral- and host-encoded proteins is a key step during the replication of positive-stranded RNA viruses in the infected cells. Previous genome-wide screens with Tomato bushy stunt tombusvirus (TBSV) in a yeast model host have revealed the involvement of eleven cellular ESCRT (endosomal sorting complexes required for transport) proteins in viral replication. The ESCRT proteins are involved in endosomal sorting of cellular membrane proteins by forming multiprotein complexes, deforming membranes away from the cytosol and, ultimately, pinching off vesicles into the lumen of the endosomes. In this paper, we show an unexpected key role for the conserved Vps4p AAA+ ATPase, whose canonical function is to disassemble the ESCRT complexes and recycle them from the membranes back to the cytosol. We find that the tombusvirus p33 replication protein interacts with Vps4p and three ESCRT-III proteins. Interestingly, Vps4p is recruited to become a permanent component of the VRCs as shown by co-purification assays and immuno-EM. Vps4p is co-localized with the viral dsRNA and contacts the viral (+)RNA in the intracellular membrane. Deletion of Vps4p in yeast leads to the formation of crescent-like membrane structures instead of the characteristic spherule and vesicle-like structures. The in vitro assembled tombusvirus replicase based on cell-free extracts (CFE) from vps4Δ yeast is highly nuclease sensitive, in contrast with the nuclease insensitive replicase in wt CFE. These data suggest that the role of Vps4p and the ESCRT machinery is to aid building the membrane-bound VRCs, which become nuclease-insensitive to avoid the recognition by the host antiviral surveillance system and the destruction of the viral RNA. Other (+)RNA viruses of plants and animals might also subvert Vps4p and the ESCRT machinery for formation of VRCs, which require membrane deformation and spherule formation. Replication of positive-stranded RNA viruses depends on recruitment of host proteins and cellular membranes to assemble the viral replicase complexes. Tombusviruses, small RNA viruses of plants, co-opt the cellular ESCRT (endosomal sorting complexes required for transport) proteins to facilitate replicase assembly on the peroxisomal membranes. The authors show a surprising role for the ESCRT-associated Vps4p AAA+ ATPase during tombusvirus replication. They show that Vps4p is recruited to and becomes a permanent member of the replicase complex through its interaction with the viral replication proteins. Also, EM and immuno-EM studies reveal that Vps4p is required for the formation of single-membrane vesicle-like structures, called spherules, which represent the sites of tombusvirus replication. The authors propose that Vps4p and other ESCRT proteins are required for membrane deformation and replicase assembly.
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Kovalev N, Nagy PD. The expanding functions of cellular helicases: the tombusvirus RNA replication enhancer co-opts the plant eIF4AIII-like AtRH2 and the DDX5-like AtRH5 DEAD-box RNA helicases to promote viral asymmetric RNA replication. PLoS Pathog 2014; 10:e1004051. [PMID: 24743583 PMCID: PMC3990711 DOI: 10.1371/journal.ppat.1004051] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2013] [Accepted: 02/19/2014] [Indexed: 12/17/2022] Open
Abstract
Replication of plus-strand RNA viruses depends on recruited host factors that aid several critical steps during replication. Several of the co-opted host factors bind to the viral RNA, which plays multiple roles, including mRNA function, as an assembly platform for the viral replicase (VRC), template for RNA synthesis, and encapsidation during infection. It is likely that remodeling of the viral RNAs and RNA-protein complexes during the switch from one step to another requires RNA helicases. In this paper, we have discovered a second group of cellular RNA helicases, including the eIF4AIII-like yeast Fal1p and the DDX5-like Dbp3p and the orthologous plant AtRH2 and AtRH5 DEAD box helicases, which are co-opted by tombusviruses. Unlike the previously characterized DDX3-like AtRH20/Ded1p helicases that bind to the 3' terminal promoter region in the viral minus-strand (-)RNA, the other class of eIF4AIII-like RNA helicases bind to a different cis-acting element, namely the 5' proximal RIII(-) replication enhancer (REN) element in the TBSV (-)RNA. We show that the binding of AtRH2 and AtRH5 helicases to the TBSV (-)RNA could unwind the dsRNA structure within the RIII(-) REN. This unique characteristic allows the eIF4AIII-like helicases to perform novel pro-viral functions involving the RIII(-) REN in stimulation of plus-strand (+)RNA synthesis. We also show that AtRH2 and AtRH5 helicases are components of the tombusvirus VRCs based on co-purification experiments. We propose that eIF4AIII-like helicases destabilize dsRNA replication intermediate within the RIII(-) REN that promotes bringing the 5' and 3' terminal (-)RNA sequences in close vicinity via long-range RNA-RNA base pairing. This newly formed RNA structure promoted by eIF4AIII helicase together with AtRH20 helicase might facilitate the recycling of the viral replicases for multiple rounds of (+)-strand synthesis, thus resulting in asymmetrical viral replication.
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Affiliation(s)
- Nikolay Kovalev
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Peter D. Nagy
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
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Abstract
UNLABELLED Replication of plus-strand RNA [(+)RNA] viruses of plants is a relatively simple process that involves complementary minus-strand RNA [(-)RNA] synthesis and subsequent (+)RNA synthesis. However, the actual replicative form of the (-)RNA template in the case of plant (+)RNA viruses is not yet established unambiguously. In this paper, using a cell-free replication assay supporting a full cycle of viral replication, we show that replication of Tomato bushy stunt virus (TBSV) leads to the formation of double-stranded RNA (dsRNA). Using RNase digestion, DNAzyme, and RNA mobility shift assays, we demonstrate the absence of naked (-)RNA templates during replication. Time course experiments showed the rapid appearance of dsRNA earlier than the bulk production of new (+)RNAs, suggesting an active role for dsRNA in replication. Radioactive nucleotide chase experiments showed that the mechanism of TBSV replication involves the use of dsRNA templates in strand displacement reactions, where the newly synthesized plus strand replaces the original (+)RNA in the dsRNA. We propose that the use of dsRNA as a template for (+)RNA synthesis by the viral replicase is facilitated by recruited host DEAD box helicases and the viral p33 RNA chaperone protein. Altogether, this replication strategy allows TBSV to separate minus- and plus-strand syntheses in time and regulate asymmetrical RNA replication that leads to abundant (+)RNA progeny. IMPORTANCE Positive-stranded RNA viruses of plants use their RNAs as the templates for replication. First, the minus strand is synthesized by the viral replicase complex (VRC), which then serves as a template for new plus-strand synthesis. To characterize the nature of the (-)RNA in the membrane-bound viral replicase, we performed complete RNA replication of Tomato bushy stunt virus (TBSV) in yeast cell-free extracts and in plant extracts. The experiments demonstrated that the TBSV (-)RNA is present as a double-stranded RNA that serves as the template for TBSV replication. During the production of new plus strands, the viral replicase displaces the old plus strand in the dsRNA template, leading to asymmetrical RNA synthesis. The presented data are in agreement with the model that the dsRNA is present in nuclease-resistant membranous VRCs. This strategy likely allows TBSV to protect the replicating viral RNA from degradation as well as to evade the early detection of viral dsRNAs by the host surveillance system.
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Rochon D, Singh B, Reade R, Theilmann J, Ghoshal K, Alam SB, Maghodia A. The p33 auxiliary replicase protein of Cucumber necrosis virus targets peroxisomes and infection induces de novo peroxisome formation from the endoplasmic reticulum. Virology 2014; 452-453:133-42. [PMID: 24606690 DOI: 10.1016/j.virol.2013.12.035] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Revised: 12/23/2013] [Accepted: 12/24/2013] [Indexed: 11/17/2022]
Abstract
Tombusviruses replicate on pre-existing organelles such as peroxisomes or mitochondria, the membranes of which become extensively reorganized into multivesicular bodies (MVBs) during the infection process. Cucumber necrosis virus (CNV) has previously been shown to replicate in association with peroxisomes in yeast. We show that CNV induces MVBs from peroxisomes in infected plants and that GFP-tagged p33 auxiliary replicase protein colocalizes with YFP(SKL), a peroxisomal marker. Most remarkably, the ER of CNV infected Nicotiana benthamiana 16C plants undergoes a dramatic reorganization producing numerous new peroxisome-like structures that associate with CNV p33, thus likely serving as a new site for viral RNA replication. We also show that plants agroinfiltrated with p33 develop CNV-like necrotic symptoms which are associated with increased levels of peroxide. Since peroxisomes are a site for peroxide catabolism, and peroxide is known to induce plant defense responses, we suggest that dysfunctional peroxisomes contribute to CNV induced necrosis.
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Affiliation(s)
- D'Ann Rochon
- Agriculture and Agri-Food Canada Pacific Agri-Food Research Centre, 4200 Hwy 97, Summerland, BC, Canada V0H 1Z0; University of British Columbia Faculty of Land and Food Systems Vancouver, BC, Canada V6T 1Z4.
| | - Bhavana Singh
- University of British Columbia Faculty of Land and Food Systems Vancouver, BC, Canada V6T 1Z4
| | - Ron Reade
- Agriculture and Agri-Food Canada Pacific Agri-Food Research Centre, 4200 Hwy 97, Summerland, BC, Canada V0H 1Z0
| | - Jane Theilmann
- Agriculture and Agri-Food Canada Pacific Agri-Food Research Centre, 4200 Hwy 97, Summerland, BC, Canada V0H 1Z0
| | - Kankana Ghoshal
- University of British Columbia Faculty of Land and Food Systems Vancouver, BC, Canada V6T 1Z4
| | - Syed Benazir Alam
- University of British Columbia Faculty of Land and Food Systems Vancouver, BC, Canada V6T 1Z4
| | - Ajay Maghodia
- Agriculture and Agri-Food Canada Pacific Agri-Food Research Centre, 4200 Hwy 97, Summerland, BC, Canada V0H 1Z0; University of British Columbia Faculty of Land and Food Systems Vancouver, BC, Canada V6T 1Z4
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Chuang C, Barajas D, Qin J, Nagy PD. Inactivation of the host lipin gene accelerates RNA virus replication through viral exploitation of the expanded endoplasmic reticulum membrane. PLoS Pathog 2014; 10:e1003944. [PMID: 24586157 PMCID: PMC3930575 DOI: 10.1371/journal.ppat.1003944] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Accepted: 01/09/2014] [Indexed: 01/27/2023] Open
Abstract
RNA viruses take advantage of cellular resources, such as membranes and lipids, to assemble viral replicase complexes (VRCs) that drive viral replication. The host lipins (phosphatidate phosphatases) are particularly interesting because these proteins play key roles in cellular decisions about membrane biogenesis versus lipid storage. Therefore, we examined the relationship between host lipins and tombusviruses, based on yeast model host. We show that deletion of PAH1 (phosphatidic acid phosphohydrolase), which is the single yeast homolog of the lipin gene family of phosphatidate phosphatases, whose inactivation is responsible for proliferation and expansion of the endoplasmic reticulum (ER) membrane, facilitates robust RNA virus replication in yeast. We document increased tombusvirus replicase activity in pah1Δ yeast due to the efficient assembly of VRCs. We show that the ER membranes generated in pah1Δ yeast is efficiently subverted by this RNA virus, thus emphasizing the connection between host lipins and RNA viruses. Thus, instead of utilizing the peroxisomal membranes as observed in wt yeast and plants, TBSV readily switches to the vastly expanded ER membranes in lipin-deficient cells to build VRCs and support increased level of viral replication. Over-expression of the Arabidopsis Pah2p in Nicotiana benthamiana decreased tombusvirus accumulation, validating that our findings are also relevant in a plant host. Over-expression of AtPah2p also inhibited the ER-based replication of another plant RNA virus, suggesting that the role of lipins in RNA virus replication might include several more eukaryotic viruses.
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Affiliation(s)
- Chingkai Chuang
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Daniel Barajas
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Jun Qin
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Peter D. Nagy
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
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Lee PKK, White KA. Construction and characterization of an aureusvirus defective RNA. Virology 2014; 452-453:67-74. [PMID: 24606684 DOI: 10.1016/j.virol.2013.12.033] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Revised: 12/08/2013] [Accepted: 12/23/2013] [Indexed: 01/30/2023]
Abstract
Defective RNAs (D RNAs) are small RNA replicons derived from viral RNA genomes. No D RNAs have been found associated with members of the plus-strand RNA virus genus Aureusvirus (family Tombusviridae). Accordingly, we sought to construct a D RNA for the aureusvirus Cucumber leaf spot virus (CLSV) using the known structure of tombusvirus defective interfering RNAs as a guide. An efficiently accumulating CLSV D RNA was generated that contained four non-contiguous regions of the viral genome and this replicon was used as a tool to studying viral cis-acting RNA elements. The results of structural and functional analyses indicated that CLSV contains counterparts for several of the major RNA elements found in tombusviruses. However, although similar, the CLSV D RNA and its components are distinct and provide insights into RNA-based specificity and mechanisms of function.
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Affiliation(s)
- Pui Kei K Lee
- Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3
| | - K Andrew White
- Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3.
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Hyodo K, Kaido M, Okuno T. Host and viral RNA-binding proteins involved in membrane targeting, replication and intercellular movement of plant RNA virus genomes. FRONTIERS IN PLANT SCIENCE 2014; 5:321. [PMID: 25071804 PMCID: PMC4083346 DOI: 10.3389/fpls.2014.00321] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Accepted: 06/18/2014] [Indexed: 05/10/2023]
Abstract
Many plant viruses have positive-strand RNA [(+)RNA] as their genome. Therefore, it is not surprising that RNA-binding proteins (RBPs) play important roles during (+)RNA virus infection in host plants. Increasing evidence demonstrates that viral and host RBPs play critical roles in multiple steps of the viral life cycle, including translation and replication of viral genomic RNAs, and their intra- and intercellular movement. Although studies focusing on the RNA-binding activities of viral and host proteins, and their associations with membrane targeting, and intercellular movement of viral genomes have been limited to a few viruses, these studies have provided important insights into the molecular mechanisms underlying the replication and movement of viral genomic RNAs. In this review, we briefly overview the currently defined roles of viral and host RBPs whose RNA-binding activity have been confirmed experimentally in association with their membrane targeting, and intercellular movement of plant RNA virus genomes.
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Affiliation(s)
| | | | - Tetsuro Okuno
- *Correspondence: Tetsuro Okuno, Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Sakyo-ku,Kyoto 606-8502, Japan e-mail:
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Hull R. Replication of Plant Viruses. PLANT VIROLOGY 2014. [PMCID: PMC7184227 DOI: 10.1016/b978-0-12-384871-0.00007-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Viruses replicate using both their own genetic information and host cell components and machinery. The different genome types have different replication pathways which contain controls on linking the process with translation and movement around the cell as well as not compromising the infected cell. This chapter discusses the replication mechanisms, faults in replication and replication of viruses co-infecting cells. Viruses replicate using both their own genetic information and host cell components and machinery. The different genome types have different replication pathways which contain controls on linking the process with translation and movement around the cell as well as not compromising the infected cell. This chapter discusses the replication mechanisms, faults in replication and replication of viruses coinfecting cells.
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[Template selection by replication protein of tobacco mosaic virus]. Uirusu 2014; 64:3-10. [PMID: 25765975 DOI: 10.2222/jsv.64.3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Replication proteins of eukaryotic positive-strand RNA viruses specifically recognize the genomic RNA as replication template, recruit them to the surfaces of intracellular membranes, and form replication complexes. We recently revealed that tobacco mosaic virus (TMV) replication protein cotranslationally binds 5' untranslated region (UTR) of the genomic RNA, and that a full-length replication protein cannot posttranslationally bind TMV RNA in trans. This result provides a mechanistic explanation for the previously reported property of TMV replication protein that it selects replication template preferentially in cis. We also found that the binding of the replication protein to the 5' UTR prevents further translation of the genomic RNA. Fatal collision between translating ribosomes and negative-strand RNA-synthesizing polymerases on the genomic RNA is thus avoided.
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Kovalev N, Nagy PD. Cyclophilin A binds to the viral RNA and replication proteins, resulting in inhibition of tombusviral replicase assembly. J Virol 2013; 87:13330-42. [PMID: 24089553 PMCID: PMC3838255 DOI: 10.1128/jvi.02101-13] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 09/24/2013] [Indexed: 01/04/2023] Open
Abstract
Replication of plus-stranded RNA viruses is greatly affected by numerous host-encoded proteins that act as restriction factors. Cyclophilins, which are a large family of cellular prolyl isomerases, have been found to inhibit Tomato bushy stunt tombusvirus (TBSV) replication in a Saccharomyces cerevisiae model based on genome-wide screens and global proteomics approaches. In this report, we further characterize single-domain cyclophilins, including the mammalian cyclophilin A and plant Roc1 and Roc2, which are orthologs of the yeast Cpr1p cyclophilin, a known inhibitor of TBSV replication in yeast. We found that recombinant CypA, Roc1, and Roc2 strongly inhibited TBSV replication in a cell-free replication assay. Additional in vitro studies revealed that CypA, Roc1, and Roc2 cyclophilins bound to the viral replication proteins, and CypA and Roc1 also bound to the viral RNA. These interactions led to inhibition of viral RNA recruitment, the assembly of the viral replicase complex, and viral RNA synthesis. A catalytically inactive mutant of CypA was also able to inhibit TBSV replication in vitro due to binding to the replication proteins and the viral RNA. Overexpression of CypA and its mutant in yeast or plant leaves led to inhibition of tombusvirus replication, confirming that CypA is a restriction factor for TBSV. Overall, the current work has revealed a regulatory role for the cytosolic single-domain Cpr1-like cyclophilins in RNA virus replication.
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Affiliation(s)
- Nikolay Kovalev
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, USA
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65
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Menzel W, Thottappilly G, Winter S. Characterization of an isometric virus isolated from yam (Dioscorea rotundata) in Nigeria suggests that it belongs to a new species in the genus Aureusvirus. Arch Virol 2013; 159:603-6. [PMID: 24085328 DOI: 10.1007/s00705-013-1845-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Accepted: 08/02/2013] [Indexed: 11/30/2022]
Affiliation(s)
- Wulf Menzel
- Plant Virus Department, Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Inhoffenstrasse 7B, 38124, Braunschweig, Germany,
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66
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Identification of novel host factors via conserved domain search: Cns1 cochaperone is a novel restriction factor of tombusvirus replication in yeast. J Virol 2013; 87:12600-10. [PMID: 24027337 DOI: 10.1128/jvi.00196-13] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
A large number of host-encoded proteins affect the replication of plus-stranded RNA viruses by acting as susceptibility factors. Many other cellular proteins are known to function as restriction factors of viral infections. Previous studies with tomato bushy stunt tombusvirus (TBSV) in a yeast model host have revealed the inhibitory function of TPR (tetratricopeptide repeat) domain-containing cyclophilins, which are members of the large family of host prolyl isomerases, in TBSV replication. In this paper, we tested additional TPR-containing yeast proteins in a cell-free TBSV replication assay and identified the Cns1p cochaperone for heat shock protein 70 (Hsp70) and Hsp90 chaperones as a strong inhibitor of TBSV replication. Cns1p interacted with the viral replication proteins and inhibited the assembly of the viral replicase complex and viral RNA synthesis in vitro. Overexpression of Cns1p inhibited TBSV replication in yeast. The use of a temperature-sensitive (TS) mutant of Cns1p in yeast revealed that at a semipermissive temperature, TS Cns1p could not inhibit TBSV replication. Interestingly, Cns1p and the TPR-containing Cpr7p cyclophilin have similar inhibitory functions during TBSV replication, although some of the details of their viral restriction mechanisms are different. Our observations indicate that TPR-containing cellular proteins could act as virus restriction factors.
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67
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Wu B, Grigull J, Ore MO, Morin S, White KA. Global organization of a positive-strand RNA virus genome. PLoS Pathog 2013; 9:e1003363. [PMID: 23717202 PMCID: PMC3662671 DOI: 10.1371/journal.ppat.1003363] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 04/02/2013] [Indexed: 12/22/2022] Open
Abstract
The genomes of plus-strand RNA viruses contain many regulatory sequences and structures that direct different viral processes. The traditional view of these RNA elements are as local structures present in non-coding regions. However, this view is changing due to the discovery of regulatory elements in coding regions and functional long-range intra-genomic base pairing interactions. The ∼4.8 kb long RNA genome of the tombusvirus tomato bushy stunt virus (TBSV) contains these types of structural features, including six different functional long-distance interactions. We hypothesized that to achieve these multiple interactions this viral genome must utilize a large-scale organizational strategy and, accordingly, we sought to assess the global conformation of the entire TBSV genome. Atomic force micrographs of the genome indicated a mostly condensed structure composed of interconnected protrusions extending from a central hub. This configuration was consistent with the genomic secondary structure model generated using high-throughput selective 2′-hydroxyl acylation analysed by primer extension (i.e. SHAPE), which predicted different sized RNA domains originating from a central region. Known RNA elements were identified in both domain and inter-domain regions, and novel structural features were predicted and functionally confirmed. Interestingly, only two of the six long-range interactions known to form were present in the structural model. However, for those interactions that did not form, complementary partner sequences were positioned relatively close to each other in the structure, suggesting that the secondary structure level of viral genome structure could provide a basic scaffold for the formation of different long-range interactions. The higher-order structural model for the TBSV RNA genome provides a snapshot of the complex framework that allows multiple functional components to operate in concert within a confined context. The genomes of many important pathogenic viruses are made of RNA. These genomes encode viral proteins and contain regulatory sequences and structures. In some viruses, distant regions of the RNA genome can interact with each other via base pairing, which suggests that certain genomes may take on well-defined conformations. This concept was investigated using a tombusvirus RNA genome that contains several long-range RNA interactions. The results of microscopic and biochemical analyses indicated a compact genome conformation with structured regions radiating from a central core. The structural model was compatible with some, but not all, long-range interactions, suggesting that the genome is a dynamic molecule that assumes different conformations. The analysis also revealed new structural features of the genome, some of which were shown to be functionally relevant. This study advances our understanding of the role played by global structure in virus genome function and provides a model to further investigate its in role virus reproduction. We anticipate that organizational principles revealed by this investigation will be applicable to other viruses.
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Affiliation(s)
- Baodong Wu
- Department of Biology, York University, Toronto, Ontario, Canada
| | - Jörg Grigull
- Department of Mathematics and Statistics, York University, Toronto, Ontario, Canada
| | - Moriam O. Ore
- Department of Chemistry, York University, Toronto, Ontario, Canada
| | - Sylvie Morin
- Department of Chemistry, York University, Toronto, Ontario, Canada
| | - K. Andrew White
- Department of Biology, York University, Toronto, Ontario, Canada
- * E-mail:
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68
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Schuck J, Gursinsky T, Pantaleo V, Burgyán J, Behrens SE. AGO/RISC-mediated antiviral RNA silencing in a plant in vitro system. Nucleic Acids Res 2013; 41:5090-103. [PMID: 23535144 PMCID: PMC3643602 DOI: 10.1093/nar/gkt193] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Accepted: 02/28/2013] [Indexed: 01/09/2023] Open
Abstract
AGO/RISC-mediated antiviral RNA silencing, an important component of the plant's immune response against RNA virus infections, was recapitulated in vitro. Cytoplasmic extracts of tobacco protoplasts were applied that supported Tombusvirus RNA replication, as well as the formation of RNA-induced silencing complexes (RISC) that could be functionally reconstituted with various plant ARGONAUTE (AGO) proteins. For example, when RISC containing AGO1, 2, 3 or 5 were programmed with exogenous siRNAs that specifically targeted the viral RNA, endonucleolytic cleavages occurred and viral replication was inhibited. Antiviral RNA silencing was disabled by the viral silencing suppressor p19 when this was present early during RISC formation. Notably, with replicating viral RNA, only (+)RNA molecules were accessible to RISC, whereas (-)RNA replication intermediates were not. The vulnerability of viral RNAs to RISC activity also depended on the RNA structure of the target sequence. This was most evident when we characterized viral siRNAs (vsiRNAs) that were particularly effective in silencing with AGO1- or AGO2/RISC. These vsiRNAs targeted similar sites, suggesting that accessible parts of the viral (+)RNA may be collectively attacked by different AGO/RISC. The in vitro system was, hence, established as a valuable tool to define and characterize individual molecular determinants of antiviral RNA silencing.
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Affiliation(s)
- Jana Schuck
- Institute of Biochemistry and Biotechnology (NFI), Martin Luther University Halle-Wittenberg, Halle/Saale D-06120, Germany, Istituto di Virologia Vegetale (IVV) del CNR, Research Unit of Bari, Bari I-70126, Italy and Agricultural Biotechnology Center, Ministry of Rural Development, Gödöllö H-2100, Hungary
| | - Torsten Gursinsky
- Institute of Biochemistry and Biotechnology (NFI), Martin Luther University Halle-Wittenberg, Halle/Saale D-06120, Germany, Istituto di Virologia Vegetale (IVV) del CNR, Research Unit of Bari, Bari I-70126, Italy and Agricultural Biotechnology Center, Ministry of Rural Development, Gödöllö H-2100, Hungary
| | - Vitantonio Pantaleo
- Institute of Biochemistry and Biotechnology (NFI), Martin Luther University Halle-Wittenberg, Halle/Saale D-06120, Germany, Istituto di Virologia Vegetale (IVV) del CNR, Research Unit of Bari, Bari I-70126, Italy and Agricultural Biotechnology Center, Ministry of Rural Development, Gödöllö H-2100, Hungary
| | - Jozsef Burgyán
- Institute of Biochemistry and Biotechnology (NFI), Martin Luther University Halle-Wittenberg, Halle/Saale D-06120, Germany, Istituto di Virologia Vegetale (IVV) del CNR, Research Unit of Bari, Bari I-70126, Italy and Agricultural Biotechnology Center, Ministry of Rural Development, Gödöllö H-2100, Hungary
| | - Sven-Erik Behrens
- Institute of Biochemistry and Biotechnology (NFI), Martin Luther University Halle-Wittenberg, Halle/Saale D-06120, Germany, Istituto di Virologia Vegetale (IVV) del CNR, Research Unit of Bari, Bari I-70126, Italy and Agricultural Biotechnology Center, Ministry of Rural Development, Gödöllö H-2100, Hungary
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69
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Usami A, Mochizuki T, Tsuda S, Ohki ST. Large-scale codon de-optimisation of the p29 replicase gene by synonymous substitutions causes a loss of infectivity of melon necrotic spot virus. Arch Virol 2013; 158:1979-85. [DOI: 10.1007/s00705-013-1683-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 02/20/2013] [Indexed: 12/27/2022]
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70
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Qiu Y, Wang Z, Liu Y, Qi N, Miao M, Si J, Xiang X, Cai D, Hu Y, Zhou X. Membrane association of Wuhan nodavirus protein A is required for its ability to accumulate genomic RNA1 template. Virology 2013; 439:140-51. [PMID: 23490047 DOI: 10.1016/j.virol.2013.02.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Revised: 01/16/2013] [Accepted: 02/13/2013] [Indexed: 01/13/2023]
Abstract
One common feature of positive-strand RNA viruses is the association of viral RNA and viral RNA replicase proteins with specific intracellular membranes to form RNA replication complexes. Wuhan nodavirus (WhNV) encodes protein A, which is the sole viral RNA replicase. Here, we showed that WhNV protein A closely associates with mitochondrial outer membranes and colocalizes with viral RNA replication sites. We further identified the transmembrane domains (N-terminal aa 33-64 and aa 212-254) of protein A for membrane association and mitochondrial localization. Moreover, we found that protein A accumulates genomic RNA by stabilizing the RNA. And our further investigation revealed that the ability of WhNV protein A to associate with membranes is closely linked with its ability for membrane recruitment and stabilization of viral genomic RNA templates. This study represents an advance toward understanding the mechanism of the RNA replication of WhNV and probably other nodaviruses.
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Affiliation(s)
- Yang Qiu
- State Key Laboratory of Virology, College of Life Sciences, Wuhan, Hubei 430072, China
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71
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Pathak KB, Jiang Z, Ochanine V, Sharma M, Pogany J, Nagy PD. Characterization of dominant-negative and temperature-sensitive mutants of tombusvirus replication proteins affecting replicase assembly. Virology 2013; 437:48-61. [PMID: 23332599 DOI: 10.1016/j.virol.2012.12.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2012] [Revised: 06/21/2012] [Accepted: 12/12/2012] [Indexed: 12/16/2022]
Abstract
The assembly of the viral replicase complex (VRC) on subcellular membranes is a key step in the replication process of plus-stranded RNA viruses. In this work, we have identified lethal and temperature sensitive (ts) point mutations within the essential p33:p33/p92 interaction domain of p33 and p92 replication proteins of Cucumber necrosis virus, a tombusvirus. Mutations within the p33:p33/p92 interaction domain also affected viral RNA recombination in yeast model host. An in vitro approach based on yeast cell free extract demonstrated that several p33 and p92 mutants behaved as dominant-negative during VRC assembly, and they showed reduced binding to the viral (+)RNA and affected activation of the p92 RdRp protein, while they did not directly influence (-) or (+)-strand synthesis. Overall, the presented data provide direct evidence that the p33:p33/p92 interaction domains in p33 and p92 are needed for the early stage of virus replication and also influence viral recombination.
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Affiliation(s)
- Kunj B Pathak
- Department of Plant Pathology, University of Kentucky, Lexington, KY 40546, USA
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72
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Mine A, Okuno T. Composition of plant virus RNA replicase complexes. Curr Opin Virol 2012; 2:669-75. [DOI: 10.1016/j.coviro.2012.09.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2012] [Revised: 09/18/2012] [Accepted: 09/27/2012] [Indexed: 01/26/2023]
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73
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Nawaz-ul-Rehman MS, Reddisiva Prasanth K, Baker J, Nagy PD. Yeast screens for host factors in positive-strand RNA virus replication based on a library of temperature-sensitive mutants. Methods 2012; 59:207-16. [PMID: 23147170 DOI: 10.1016/j.ymeth.2012.11.001] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2012] [Revised: 10/23/2012] [Accepted: 11/01/2012] [Indexed: 12/14/2022] Open
Abstract
RNA viruses exploit host cells by altering cellular pathways, recruiting host factors, remodeling intracellular membranes and escaping host antiviral responses. Model hosts, such as Saccharomyces cerevisiae (yeast), are valuable to identify host factors involved in viral RNA replication. The many advantages of using yeast include the availability of various yeast mutant libraries, such as (i) single gene-deletion library; (ii) the essential gene library (yTHC); and (iii) the yeast ORF over-expression library. Here, we have used a novel temperature-sensitive (ts) mutant library of essential yeast genes to identify 118 host proteins affecting replication of Tomato bushy stunt virus, in yeast model host. Testing 787 ts mutants led to the identification of host factors, of which 72 proteins facilitated TBSV replication in yeast and 46 proteins were inhibitory. Altogether, ~85% of the identified proteins are novel host factors affecting tombusvirus replication. The ts mutant library screen also led to the identification of 17 essential genes, which have been documented before, thus confirming the importance of these genomic screens. Overall, we show the power of ts mutant library in identification of host factors for RNA virus replication.
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74
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Nagy PD, Barajas D, Pogany J. Host factors with regulatory roles in tombusvirus replication. Curr Opin Virol 2012; 2:691-8. [PMID: 23122856 DOI: 10.1016/j.coviro.2012.10.004] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Revised: 10/02/2012] [Accepted: 10/06/2012] [Indexed: 11/27/2022]
Abstract
Similar to animal viruses, the abundant plant positive-strand RNA viruses replicate in infected cells by exploiting the vast resources of the host. This review focuses on virus-host interactions during tombusvirus replication. The multifunctional tombusvirus p33 replication protein not only interacts with itself, the viral p92(pol) polymerase, and viral RNA, but also with approximately 100 cellular proteins and subcellular membranes. Several negative regulatory host proteins, such as cyclophilins and WW motif containing proteins, also bind to p33 and interfere with p33's functions. To explain how p33 can perform multiple functions, we propose that a variety of interactions involving p33 result in the commitment of p33 molecules to specific tasks. This facilitates tight spatial and temporal organization of viral replication in infected cells.
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Affiliation(s)
- Peter D Nagy
- Department of Plant Pathology, University of Kentucky, Lexington, KY 40546, USA.
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75
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Mine A, Hyodo K, Tajima Y, Kusumanegara K, Taniguchi T, Kaido M, Mise K, Taniguchi H, Okuno T. Differential roles of Hsp70 and Hsp90 in the assembly of the replicase complex of a positive-strand RNA plant virus. J Virol 2012; 86:12091-104. [PMID: 22933272 PMCID: PMC3486462 DOI: 10.1128/jvi.01659-12] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Accepted: 08/21/2012] [Indexed: 02/06/2023] Open
Abstract
Assembly of viral replicase complexes of eukaryotic positive-strand RNA viruses is a regulated process: multiple viral and host components must be assembled on intracellular membranes and ordered into quaternary complexes capable of synthesizing viral RNAs. However, the molecular mechanisms underlying this process are poorly understood. In this study, we used a model virus, Red clover necrotic mosaic virus (RCNMV), whose replicase complex can be detected readily as the 480-kDa functional protein complex. We found that host heat shock proteins Hsp70 and Hsp90 are required for RCNMV RNA replication and that they interact with p27, a virus-encoded component of the 480-kDa replicase complex, on the endoplasmic reticulum membrane. Using a cell-free viral translation/replication system in combination with specific inhibitors of Hsp70 and Hsp90, we found that inhibition of p27-Hsp70 interaction inhibits the formation of the 480-kDa complex but instead induces the accumulation of large complexes that are nonfunctional in viral RNA synthesis. In contrast, inhibition of p27-Hsp90 interaction did not induce such large complexes but rendered p27 incapable of binding to a specific viral RNA element, which is a critical step for the assembly of the 480-kDa replicase complex and viral RNA replication. Together, our results suggest that Hsp70 and Hsp90 regulate different steps in the assembly of the RCNMV replicase complex.
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Affiliation(s)
- Akira Mine
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
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76
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Authentic in vitro replication of two tombusviruses in isolated mitochondrial and endoplasmic reticulum membranes. J Virol 2012; 86:12779-94. [PMID: 22973028 DOI: 10.1128/jvi.00973-12] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Replication of plus-stranded RNA viruses takes place on membranous structures derived from various organelles in infected cells. Previous works with Tomato bushy stunt tombusvirus (TBSV) revealed the recruitment of either peroxisomal or endoplasmic reticulum (ER) membranes for replication. In case of Carnation Italian ringspot tombusvirus (CIRV), the mitochondrial membranes supported CIRV replication. In this study, we developed ER and mitochondrion-based in vitro tombusvirus replication assays. Using purified recombinant TBSV and CIRV replication proteins, we showed that TBSV could use the purified yeast ER and mitochondrial preparations for complete viral RNA replication, while CIRV preferentially replicated in the mitochondrial membranes. The viral RNA became partly RNase resistant after ∼40 to 60 min of incubation in the purified ER and mitochondrial preparations, suggesting that assembly of TBSV and CIRV replicases could take place in the purified ER and mitochondrial membranes in vitro. Using chimeric and heterologous combinations of replication proteins, we showed that multiple domains within the replication proteins are involved in determining the efficiency of tombusvirus replication in the two subcellular membranes. Altogether, we demonstrated that TBSV is less limited while CIRV is more restricted in utilizing various intracellular membranes for replication. Overall, the current work provides evidence that tombusvirus replication could occur in vitro in isolated subcellular membranes, suggesting that tombusviruses have the ability to utilize alternative organellar membranes during infection that could increase the chance of mixed virus replication and rapid evolution during coinfection.
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77
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Shah Nawaz-ul-Rehman M, Martinez-Ochoa N, Pascal H, Sasvari Z, Herbst C, Xu K, Baker J, Sharma M, Herbst A, Nagy PD. Proteome-wide overexpression of host proteins for identification of factors affecting tombusvirus RNA replication: an inhibitory role of protein kinase C. J Virol 2012; 86:9384-95. [PMID: 22718827 PMCID: PMC3416130 DOI: 10.1128/jvi.00019-12] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2012] [Accepted: 06/13/2012] [Indexed: 01/08/2023] Open
Abstract
To identify host genes affecting replication of Tomato bushy stunt virus (TBSV), a small model positive-stranded RNA virus, we overexpressed 5,500 yeast proteins individually in Saccharomyces cerevisiae, which supports TBSV replication. In total, we identified 141 host proteins, and overexpression of 40 of those increased and the remainder decreased the accumulation of a TBSV replicon RNA. Interestingly, 36 yeast proteins were identified previously by various screens, greatly strengthening the relevance of these host proteins in TBSV replication. To validate the results from the screen, we studied the effect of protein kinase C1 (Pkc1), a conserved host kinase involved in many cellular processes, which inhibited TBSV replication when overexpressed. Using a temperature-sensitive mutant of Pkc1p revealed a high level of TBSV replication at a semipermissive temperature, further supporting the idea that Pkc1p is an inhibitor of TBSV RNA replication. A direct inhibitory effect of Pkc1p was shown in a cell-free yeast extract-based TBSV replication assay, in which Pkc1p likely phosphorylates viral replication proteins, decreasing their abilities to bind to the viral RNA. We also show that cercosporamide, a specific inhibitor of Pkc-like kinases, leads to increased TBSV replication in yeast, in plant single cells, and in whole plants, suggesting that Pkc-related pathways are potent inhibitors of TBSV in several hosts.
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78
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p33-Independent activation of a truncated p92 RNA-dependent RNA polymerase of Tomato bushy stunt virus in yeast cell-free extract. J Virol 2012; 86:12025-38. [PMID: 22933278 DOI: 10.1128/jvi.01303-12] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Plus-stranded RNA viruses replicate in membrane-bound structures containing the viral replicase complex (VRC). A key component of the VRC is the virally encoded RNA-dependent RNA polymerase (RdRp), which should be activated and incorporated into the VRC after its translation. To study the activation of the RdRp of Tomato bushy stunt virus (TBSV), a small tombusvirus of plants, we used N-terminal truncated recombinant RdRp, which supported RNA synthesis in a cell-free yeast extract-based assay. The truncated RdRp required a cis-acting RNA replication element and soluble host factors, while unlike the full-length TBSV RdRp, the truncated RdRp did not need the viral p33 replication cofactor or cellular membranes for RNA synthesis. Interestingly, the truncated RdRp used 3'-terminal extension for initiation and terminated prematurely at an internal cis-acting element. However, the truncated RdRp could perform de novo initiation on a TBSV plus-strand RNA template in the presence of the p33 replication cofactor, cellular membranes, and soluble host proteins. Altogether, the data obtained with the truncated RdRp indicate that this RdRp still requires activation, but with the participation of fewer components than with the full-length RdRp, making it suitable for future studies on dissection of the RdRp activation mechanism.
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79
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Nicholson BL, Lee PKK, White KA. Internal RNA Replication Elements are Prevalent in Tombusviridae. Front Microbiol 2012; 3:279. [PMID: 22888327 PMCID: PMC3412338 DOI: 10.3389/fmicb.2012.00279] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Accepted: 07/17/2012] [Indexed: 01/09/2023] Open
Abstract
Internal replication elements (IREs) are RNA structures that are present at internal positions in the genomes of different types of plus-strand RNA viruses. Members of the genus Tombusvirus (family Tombusviridae) contain an IRE within the polymerase coding region of their genomes and this RNA element participates in both genome targeting to sites of replication and replicase complex assembly. Here we propose that other members of the virus family Tombusviridae also possess comparable IREs. Through sequence and structural analyses, candidate IREs in several genera of this family were identified, including aureusviruses, necroviruses, carmoviruses, and pelarspoviruses. The results from subsequent mutational analysis of selected proposed IREs were consistent with a critical role for these structures in viral genome accumulation during infections. Our study supports the existence of IREs in several genera in Tombusviridae and points to previously unappreciated similarities in genome replication strategies between members of this virus family.
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80
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Kovalev N, Barajas D, Nagy PD. Similar roles for yeast Dbp2 and Arabidopsis RH20 DEAD-box RNA helicases to Ded1 helicase in tombusvirus plus-strand synthesis. Virology 2012; 432:470-84. [PMID: 22832121 DOI: 10.1016/j.virol.2012.06.030] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Revised: 05/17/2012] [Accepted: 06/28/2012] [Indexed: 01/05/2023]
Abstract
Recruited host factors aid replication of plus-strand RNA viruses. In this paper, we show that Dbp2 DEAD-box helicase of yeast, which is a homolog of human p68 DEAD-box helicase, directly affects replication of Tomato bushy stunt virus (TBSV). We demonstrate that Dbp2 binds to the 3'-end of the viral minus-stranded RNA and enhances plus-strand synthesis by the viral replicase in a yeast-based cell-free TBSV replication assay. In vitro data with wt and an ATPase-deficient Dbp2 mutant indicate that Dbp2 unwinds local secondary structures at the 3'-end of the TBSV (-)RNA. We also show that Dbp2 complements the replication deficiency of TBSV in yeast containing reduced amount of Ded1 DEAD-box helicase, another host factor involved in TBSV replication, suggesting that Dbp2 and Ded1 helicases play redundant roles in TBSV replication. We also show that the orthologous AtRH20 DEAD-box helicase from Arabidopsis can increase tombusvirus replication in vitro and in yeast.
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Affiliation(s)
- Nikolay Kovalev
- Department of Plant Pathology, University of Kentucky, Lexington, KY 40546, United States
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81
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Rubino L, Russo M. A single amino acid substitution in the ORF1 of cymbidium ringspot virus determines the accumulation of two satellite RNAs. Virus Res 2012; 168:84-7. [PMID: 22709553 DOI: 10.1016/j.virusres.2012.06.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Revised: 06/04/2012] [Accepted: 06/08/2012] [Indexed: 11/24/2022]
Abstract
Tombusviruses may support the replication of satellite (sat) RNAs. In particular, two satRNAs, sat L and Cymsat RNAs, are replicated by carnation Italian ringspot (CIRV) and tomato bushy stunt (TBSV) virus, but not by cymbidium ringspot virus (CymRSV) in vitro transcripts unless they contain a poly(A) tail at the 3' end. Conversely, the replication of both satRNAs was supported by virus particles or viral RNA of the original CymRSV inoculum even in the absence of the poly(A) tail. Sequence and mutational analyses revealed that the full-length infectious CymRSV clone contains one relevant sequence variation in the ORF 1-encoded protein (p33) compared with the original inoculum, i.e. a Ser₁₉ TCC codon instead of a Phe₁₉ TTC codon, which inhibited the replication of sat L and Cymsat RNAs. It is suggested that this amino acid is contained in a domain essential for the replication of some subviral RNAs.
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Affiliation(s)
- Luisa Rubino
- Istituto di Virologia Vegetale del CNR, Unità Organizzativa di Bari, Via Amendola 165/A, 70126 Bari, Italy.
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82
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Chen HC, Kong LR, Yeh TY, Cheng CP, Hsu YH, Lin NS. The conserved 5' apical hairpin stem loops of bamboo mosaic virus and its satellite RNA contribute to replication competence. Nucleic Acids Res 2012; 40:4641-52. [PMID: 22278884 PMCID: PMC3378871 DOI: 10.1093/nar/gks030] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2011] [Revised: 12/30/2011] [Accepted: 01/05/2012] [Indexed: 11/29/2022] Open
Abstract
Satellite RNAs associated with Bamboo mosaic virus (satBaMVs) depend on BaMV for replication and encapsidation. Certain satBaMVs isolated from natural fields significantly interfere with BaMV replication. The 5' apical hairpin stem loop (AHSL) of satBaMV is the major determinant in interference with BaMV replication. In this study, by in vivo competition assay, we revealed that the sequence and structure of AHSL, along with specific nucleotides (C(60) and C(83)) required for interference with BaMV replication, are also involved in replication competition among satBaMV variants. Moreover, all of the 5' ends of natural BaMV isolates contain the similar AHSLs having conserved nucleotides (C(64) and C(86)) with those of interfering satBaMVs, suggesting their co-evolution. Mutational analyses revealed that C(86) was essential for BaMV replication, and that replacement of C(64) with U reduced replication efficiency. The non-interfering satBaMV interfered with BaMV replication with the BaMV-C64U mutant as helper. These findings suggest that two cytosines at the equivalent positions in the AHSLs of BaMV and satBaMV play a crucial role in replication competence. The downregulation level, which is dependent upon the molar ratio of interfering satBaMV to BaMV, implies that there is competition for limited replication machinery.
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Affiliation(s)
- Hsin-Chuan Chen
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei and Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
| | - Lih-Ren Kong
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei and Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
| | - Ting-Yu Yeh
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei and Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
| | - Chi-Ping Cheng
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei and Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
| | - Yau-Heiu Hsu
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei and Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
| | - Na-Sheng Lin
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei and Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
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83
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Kovalev N, Pogany J, Nagy PD. A Co-Opted DEAD-Box RNA helicase enhances tombusvirus plus-strand synthesis. PLoS Pathog 2012; 8:e1002537. [PMID: 22359508 PMCID: PMC3280988 DOI: 10.1371/journal.ppat.1002537] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Accepted: 01/03/2012] [Indexed: 01/09/2023] Open
Abstract
Replication of plus-strand RNA viruses depends on recruited host factors that aid several critical steps during replication. In this paper, we show that an essential translation factor, Ded1p DEAD-box RNA helicase of yeast, directly affects replication of Tomato bushy stunt virus (TBSV). To separate the role of Ded1p in viral protein translation from its putative replication function, we utilized a cell-free TBSV replication assay and recombinant Ded1p. The in vitro data show that Ded1p plays a role in enhancing plus-strand synthesis by the viral replicase. We also find that Ded1p is a component of the tombusvirus replicase complex and Ded1p binds to the 3′-end of the viral minus-stranded RNA. The data obtained with wt and ATPase deficient Ded1p mutants support the model that Ded1p unwinds local structures at the 3′-end of the TBSV (−)RNA, rendering the RNA compatible for initiation of (+)-strand synthesis. Interestingly, we find that Ded1p and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which is another host factor for TBSV, play non-overlapping functions to enhance (+)-strand synthesis. Altogether, the two host factors enhance TBSV replication synergistically by interacting with the viral (−)RNA and the replication proteins. In addition, we have developed an in vitro assay for Flock house virus (FHV), a small RNA virus of insects, that also demonstrated positive effect on FHV replicase activity by the added Ded1p helicase. Thus, two small RNA viruses, which do not code for their own helicases, seems to recruit a host RNA helicase to aid their replication in infected cells. Subverted host factors play a role in plus-strand RNA virus replication. Small RNA viruses do not code for their own helicases and they might recruit host RNA helicases to aid their replication in infected cells. In this paper, the authors show that the Ded1p DEAD-box helicase, which is an essential translation factor in yeast, is recruited by Tomato bushy stunt virus (TBSV) into its replicase complex. They also show that Ded1p binds to the viral (−)RNA and promotes (+)-strand TBSV synthesis when added to a yeast-based cell-free extract depleted for Ded1p. An ATPase defective Ded1p mutant failed to promote TBSV replication in vitro, suggesting that the helicase activity of Ded1p is essential for its function during TBSV replication. In addition, the authors also show that another host protein, which also binds to the (−)RNA, namely glyceraldehyde-3-phosphate dehydrogenase (GAPDH), further enhances TBSV (+)RNA when added together with Ded1p to yeast-based cell-free extract. In summary, the authors show that the major functions of Ded1p and GAPDH host proteins are to promote TBSV replication via selectively enhancing (+)-strand synthesis.
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Affiliation(s)
- Nikolay Kovalev
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Judit Pogany
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Peter D. Nagy
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
- * E-mail:
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84
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Martínez-Turiño S, Hernández C. Analysis of the subcellular targeting of the smaller replicase protein of Pelargonium flower break virus. Virus Res 2012; 163:580-91. [PMID: 22222362 DOI: 10.1016/j.virusres.2011.12.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2011] [Revised: 12/13/2011] [Accepted: 12/16/2011] [Indexed: 12/30/2022]
Abstract
Replication of all positive RNA viruses occurs in association with intracellular membranes. In many cases, the mechanism of membrane targeting is unknown and there appears to be no correlation between virus phylogeny and the membrane systems recruited for replication. Pelargonium flower break virus (PFBV, genus Carmovirus, family Tombusviridae) encodes two proteins, p27 and its read-through product p86 (the viral RNA dependent-RNA polymerase), that are essential for replication. Recent reports with other members of the family Tombusviridae have shown that the smaller replicase protein is targeted to specific intracellular membranes and it is assumed to determine the subcellular localization of the replication complex. Using in vivo expression of green fluorescent protein (GFP) fusions in plant and yeast cells, we show here that PFBV p27 localizes in mitochondria. The same localization pattern was found for p86 that contains the p27 sequence at its N-terminus. Cellular fractionation of p27GFP-expressing cells confirmed the confocal microscopy observations and biochemical treatments suggested a tight association of the protein to membranes. Analysis of deletion mutants allowed identification of two regions required for targeting of p27 to mitochondria. These regions mapped toward the N- and C-terminus of the protein, respectively, and could function independently though with distinct efficiency. In an attempt to search for putative cellular factors involved in p27 localization, the subcellular distribution of the protein was checked in a selected series of knockout yeast strains and the outcome of this approach is discussed.
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Affiliation(s)
- Sandra Martínez-Turiño
- Instituto de Biología Molecular y Celular de Plantas (CSIC-Universidad Politécnica de Valencia), Ciudad Politécnica de Innovación, Ed. 8E, Camino de Vera s/n, 46022 Valencia, Spain
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85
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Lin JY, Mendu V, Pogany J, Qin J, Nagy PD. The TPR domain in the host Cyp40-like cyclophilin binds to the viral replication protein and inhibits the assembly of the tombusviral replicase. PLoS Pathog 2012. [PMID: 22346747 DOI: 10.1371/journal.ppat.100249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/10/2023] Open
Abstract
Replication of plus-stranded RNA viruses is greatly affected by numerous host-coded proteins acting either as susceptibility or resistance factors. Previous genome-wide screens and global proteomics approaches with Tomato bushy stunt tombusvirus (TBSV) in a yeast model host revealed the involvement of cyclophilins, which are a large family of host prolyl isomerases, in TBSV replication. In this paper, we identified those members of the large cyclophilin family that interacted with the viral replication proteins and inhibited TBSV replication. Further characterization of the most effective cyclophilin, the Cyp40-like Cpr7p, revealed that it strongly inhibits many steps during TBSV replication in a cell-free replication assay. These steps include viral RNA recruitment inhibited via binding of Cpr7p to the RNA-binding region of the viral replication protein; the assembly of the viral replicase complex and viral RNA synthesis. Since the TPR (tetratricopeptide repeats) domain, but not the catalytic domain of Cpr7p is needed for the inhibitory effect on TBSV replication, it seems that the chaperone activity of Cpr7p provides the negative regulatory function. We also show that three Cyp40-like proteins from plants can inhibit TBSV replication in vitro and Cpr7p is also effective against Nodamura virus, an insect pathogen. Overall, the current work revealed a role for Cyp40-like proteins and their TPR domains as regulators of RNA virus replication.
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Affiliation(s)
- Jing-Yi Lin
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
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86
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Lin JY, Mendu V, Pogany J, Qin J, Nagy PD. The TPR domain in the host Cyp40-like cyclophilin binds to the viral replication protein and inhibits the assembly of the tombusviral replicase. PLoS Pathog 2012; 8:e1002491. [PMID: 22346747 PMCID: PMC3276564 DOI: 10.1371/journal.ppat.1002491] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Accepted: 12/04/2011] [Indexed: 12/24/2022] Open
Abstract
Replication of plus-stranded RNA viruses is greatly affected by numerous host-coded proteins acting either as susceptibility or resistance factors. Previous genome-wide screens and global proteomics approaches with Tomato bushy stunt tombusvirus (TBSV) in a yeast model host revealed the involvement of cyclophilins, which are a large family of host prolyl isomerases, in TBSV replication. In this paper, we identified those members of the large cyclophilin family that interacted with the viral replication proteins and inhibited TBSV replication. Further characterization of the most effective cyclophilin, the Cyp40-like Cpr7p, revealed that it strongly inhibits many steps during TBSV replication in a cell-free replication assay. These steps include viral RNA recruitment inhibited via binding of Cpr7p to the RNA-binding region of the viral replication protein; the assembly of the viral replicase complex and viral RNA synthesis. Since the TPR (tetratricopeptide repeats) domain, but not the catalytic domain of Cpr7p is needed for the inhibitory effect on TBSV replication, it seems that the chaperone activity of Cpr7p provides the negative regulatory function. We also show that three Cyp40-like proteins from plants can inhibit TBSV replication in vitro and Cpr7p is also effective against Nodamura virus, an insect pathogen. Overall, the current work revealed a role for Cyp40-like proteins and their TPR domains as regulators of RNA virus replication.
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Affiliation(s)
- Jing-Yi Lin
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Venugopal Mendu
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Judit Pogany
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Jun Qin
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Peter D. Nagy
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
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87
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Sasvari Z, Nagy PD. Identification of small molecule inhibitors of Tomato bushy stunt virus replication. Methods Mol Biol 2012; 894:345-57. [PMID: 22678591 DOI: 10.1007/978-1-61779-882-5_23] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The identification of small molecule inhibitors of plant virus RNA replication is useful to develop antiviral drugs and to dissect various steps in the replication process. Moreover, small molecule inhibitors could be effective tools to study similarities in replication strategies of various RNA viruses. By using Tomato bushy stunt virus (TBSV), we tested the effect of various inhibitors of host factors known to facilitate TBSV replication as well as acridine and phenanthridine derivatives, which are known anti-prion compounds, on TBSV replication. In this chapter, the methodology used to identify the direct targets of the chemicals during the different steps of replication of TBSV is described.
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Affiliation(s)
- Zsuzsanna Sasvari
- Department of Plant Pathology, University of Kentucky, Lexington, KY, USA
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88
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Nagy PD, Pogany J. The dependence of viral RNA replication on co-opted host factors. Nat Rev Microbiol 2011; 10:137-49. [PMID: 22183253 PMCID: PMC7097227 DOI: 10.1038/nrmicro2692] [Citation(s) in RCA: 323] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Positive-sense RNA ((+)RNA) viruses such as hepatitis C virus exploit host cells by subverting host proteins, remodelling subcellular membranes, co-opting and modulating protein and ribonucleoprotein complexes, and altering cellular metabolic pathways during infection. To facilitate RNA replication, (+)RNA viruses interact with numerous host molecules through protein-protein, RNA-protein and protein-lipid interactions. These interactions lead to the formation of viral replication complexes, which produce new viral RNA progeny in host cells. This Review presents the recent progress that has been made in understanding the role of co-opted host proteins and membranes during (+)RNA virus replication, and discusses common themes employed by different viruses.
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Affiliation(s)
- Peter D Nagy
- Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, Lexington, Kentucky 40546, USA.
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89
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Synergistic roles of eukaryotic translation elongation factors 1Bγ and 1A in stimulation of tombusvirus minus-strand synthesis. PLoS Pathog 2011; 7:e1002438. [PMID: 22194687 PMCID: PMC3240602 DOI: 10.1371/journal.ppat.1002438] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2011] [Accepted: 10/31/2011] [Indexed: 12/26/2022] Open
Abstract
Host factors are recruited into viral replicase complexes to aid replication of plus-strand RNA viruses. In this paper, we show that deletion of eukaryotic translation elongation factor 1Bgamma (eEF1Bγ) reduces Tomato bushy stunt virus (TBSV) replication in yeast host. Also, knock down of eEF1Bγ level in plant host decreases TBSV accumulation. eEF1Bγ binds to the viral RNA and is one of the resident host proteins in the tombusvirus replicase complex. Additional in vitro assays with whole cell extracts prepared from yeast strains lacking eEF1Bγ demonstrated its role in minus-strand synthesis by opening of the structured 3′ end of the viral RNA and reducing the possibility of re-utilization of (+)-strand templates for repeated (-)-strand synthesis within the replicase. We also show that eEF1Bγ plays a synergistic role with eukaryotic translation elongation factor 1A in tombusvirus replication, possibly via stimulation of the proper positioning of the viral RNA-dependent RNA polymerase over the promoter region in the viral RNA template.These roles for translation factors during TBSV replication are separate from their canonical roles in host and viral protein translation. RNA viruses recruit numerous host proteins to facilitate their replication and spread. Among the identified host proteins are RNA-binding proteins (RBPs), such as ribosomal proteins, translation factors and RNA-modifying enzymes. In this paper, the authors show that deletion of eukaryotic translation elongation factor 1Bgamma (eEF1Bγ) reduces Tomato bushy stunt virus (TBSV) replication in a yeast model host. Knock down of eEF1Bγ level in plant host also decreases TBSV accumulation. Moreover, the authors demonstrate that eEF1Bγ binds to the viral RNA and is present in the tombusvirus replicase complex. Functional studies revealed that eEF1Bγ promotes minus-strand synthesis by serving as an RNA chaperone. The authors also show that eEF1Bγ and eukaryotic translation elongation factor 1A, another host factor, function together to promote tombusvirus replication.
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90
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Cimino PA, Nicholson BL, Wu B, Xu W, White KA. Multifaceted regulation of translational readthrough by RNA replication elements in a tombusvirus. PLoS Pathog 2011; 7:e1002423. [PMID: 22174683 PMCID: PMC3234231 DOI: 10.1371/journal.ppat.1002423] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2011] [Accepted: 10/22/2011] [Indexed: 11/18/2022] Open
Abstract
Translational readthrough of stop codons by ribosomes is a recoding event used by a variety of viruses, including plus-strand RNA tombusviruses. Translation of the viral RNA-dependent RNA polymerase (RdRp) in tombusviruses is mediated using this strategy and we have investigated this process using a variety of in vitro and in vivo approaches. Our results indicate that readthrough generating the RdRp requires a novel long-range RNA-RNA interaction, spanning a distance of ∼3.5 kb, which occurs between a large RNA stem-loop located 3'-proximal to the stop codon and an RNA replication structure termed RIV at the 3'-end of the viral genome. Interestingly, this long-distance RNA-RNA interaction is modulated by mutually-exclusive RNA structures in RIV that represent a type of RNA switch. Moreover, a different long-range RNA-RNA interaction that was previously shown to be necessary for viral RNA replicase assembly was also required for efficient readthrough production of the RdRp. Accordingly, multiple replication-associated RNA elements are involved in modulating the readthrough event in tombusviruses and we propose an integrated mechanistic model to describe how this regulatory network could be advantageous by (i) providing a quality control system for culling truncated viral genomes at an early stage in the replication process, (ii) mediating cis-preferential replication of viral genomes, and (iii) coordinating translational readthrough of the RdRp with viral genome replication. Based on comparative sequence analysis and experimental data, basic elements of this regulatory model extend to other members of Tombusviridae, as well as to viruses outside of this family. Viruses use many different strategies to produce their proteins and some viral proteins are made with terminal extensions that confer unique properties. The polymerase that replicates the RNA genomes of tombusviruses is an extended version of another viral protein and is generated by a process called translational readthrough. We have determined the regulatory mechanism that modulates the production of this viral polymerase. Our results show that control of the readthrough process is complex and involves both local structures and long-range interactions within the viral genome. This system is also integrated with viral RNA replication elements and this allows the virus to coordinate polymerase production with genome replication. This regulatory scheme appears to represent a common tactic used by a variety of viruses.
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Affiliation(s)
- Peter A. Cimino
- Department of Biology, York University, Toronto, Ontario, Canada
| | | | - Baodong Wu
- Department of Biology, York University, Toronto, Ontario, Canada
| | - Wei Xu
- Department of Biology, York University, Toronto, Ontario, Canada
| | - K. Andrew White
- Department of Biology, York University, Toronto, Ontario, Canada
- * E-mail:
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91
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Pathak KB, Pogany J, Nagy PD. Non-template functions of the viral RNA in plant RNA virus replication. Curr Opin Virol 2011; 1:332-8. [PMID: 22440835 DOI: 10.1016/j.coviro.2011.09.011] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Revised: 09/23/2011] [Accepted: 09/26/2011] [Indexed: 10/16/2022]
Abstract
In addition to the essential function of the viral RNA as a template during replication of positive-stranded (+)RNA viruses, the RNA also has crucial non-template functions. These functions during replication include the recruitment of the viral RNA to the site of replication and assembly of the functional viral replicase complex. The RNA recruitment elements are specifically recognized by the viral replication protein, but also affected by host factors such as elongation factor 1A or P-body proteins. The cis-elements for replicase assembly can partially overlap with RNA recruitment elements and they may provide a platform for the assembly of the replicase complex consisting of viral and host proteins. This review focuses on our current knowledge obtained with tombusviruses and other plant viruses. Altogether, understanding of the non-template functions of the viral RNA during viral replication provides new insights into virus-host interactions.
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Affiliation(s)
- Kunj B Pathak
- Department of Plant Pathology, University of Kentucky, Lexington, KY 40546, USA
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92
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Defining the roles of cis-acting RNA elements in tombusvirus replicase assembly in vitro. J Virol 2011; 86:156-71. [PMID: 22013057 DOI: 10.1128/jvi.00404-11] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In addition to its central role as a template for replication and translation, the viral plus-strand RNA genome also has nontemplate functions, such as recruitment to the site of replication and assembly of the viral replicase, activities that are mediated by cis-acting RNA elements within viral genomes. Two noncontiguous RNA elements, RII(+)-SL (located internally in the tombusvirus genome) and RIV (located at the 3'-terminus), are involved in template recruitment into replication and replicase assembly; however, the importance of each of these RNA elements for these two distinct functions is not fully elucidated. We used an in vitro replicase assembly assay based on yeast cell extract and purified recombinant tombusvirus replication proteins to show that RII(+)-SL, in addition to its known requirement for recruitment of the plus-strand RNA into replication, is also necessary for assembly of an active viral replicase complex. Additional studies using a novel two-component RNA system revealed that the recruitment function of RII(+)-SL can be provided in trans by a separate RNA and that the replication silencer element, located within RIV, defines the template that is used for initiation of minus-strand synthesis. Collectively, this work has revealed new functions for tombusvirus cis-acting RNA elements and provided insights into the pioneering round of minus-strand synthesis.
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93
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Identification of amino acids in auxiliary replicase protein p27 critical for its RNA-binding activity and the assembly of the replicase complex in Red clover necrotic mosaic virus. Virology 2011; 413:300-9. [PMID: 21440279 DOI: 10.1016/j.virol.2011.02.017] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Revised: 02/04/2011] [Accepted: 02/20/2011] [Indexed: 01/17/2023]
Abstract
The specific recognition of genomic RNAs by viral replicase proteins is a key regulatory step during the early replication process in positive-strand RNA viruses. In this study, we characterized the RNA-binding activity of the auxiliary replicase protein p27 of Red clover necrotic mosaic virus (RCNMV), which has a bipartite genome consisting of RNA1 and RNA2. Aptamer pull-down assays identified the amino acid residues of p27 involved in its specific interaction with RNA2. The RNA-binding activity of p27 correlated with its activity in recruiting RNA2 to membranes. We also identified the amino acids required for the formation of the 480-kDa replicase complex, a key player of RCNMV RNA replication. These amino acids are not involved in the functions of p27 that bind viral RNA or replicase proteins, suggesting an additional role for p27 in the assembly of the replicase complex. Our results demonstrate that p27 has multiple functions in RCNMV replication.
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94
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Abstract
Plus-strand +RNA viruses co-opt host RNA-binding proteins (RBPs) to perform many functions during viral replication. A few host RBPs have been identified that affect the recruitment of viral +RNAs for replication. Other subverted host RBPs help the assembly of the membrane-bound replicase complexes, regulate the activity of the replicase and control minus- or plus-strand RNA synthesis. The host RBPs also affect the stability of viral RNAs, which have to escape cellular RNA degradation pathways. While many host RBPs seem to have specialized functions, others participate in multiple events during infection. Several conserved RBPs, such as eEF1A, hnRNP proteins and Lsm 1-7 complex, are co-opted by evolutionarily diverse +RNA viruses, underscoring some common themes in virus-host interactions. On the other hand, viruses also hijack unique RBPs, suggesting that +RNA viruses could utilize different RBPs to perform similar functions. Moreover, different +RNA viruses have adapted unique strategies for co-opting unique RBPs. Altogether, a deeper understanding of the functions of the host RBPs subverted for viral replication will help development of novel antiviral strategies and give new insights into host RNA biology.
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Affiliation(s)
- Zhenghe Li
- Department of Plant Pathology, University of Kentucky, Lexington, KY, USA
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95
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Abstract
RNA viruses are the champions of evolution due to high frequency mutations and genetic recombination occurring during virus replication. These genetic events are due to the error-prone nature of viral RNA-dependent RNA polymerases (RdRp). Recently emerging models on viral RNA recombination, however, also include key roles for host and environmental factors. Accordingly, genome-wide screens and global proteomics approaches with Tomato bushy stunt virus (TBSV) and yeast (Saccharomyces cerevisiae) as a model host have identified 38 host proteins affecting viral RNA recombination. Follow-up studies have identified key host proteins and cellular pathways involved in TBSV RNA recombination. In addition, environmental factors, such as salt stress, have been shown to affect TBSV recombination via influencing key host or viral factors involved in the recombination process. These advances will help build more accurate models on viral recombination, evolution, and adaptation.
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96
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Iwakawa HO, Mine A, Hyodo K, An M, Kaido M, Mise K, Okuno T. Template recognition mechanisms by replicase proteins differ between bipartite positive-strand genomic RNAs of a plant virus. J Virol 2011; 85:497-509. [PMID: 20980498 PMCID: PMC3014169 DOI: 10.1128/jvi.01754-10] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2010] [Accepted: 10/21/2010] [Indexed: 01/14/2023] Open
Abstract
Recognition of RNA templates by viral replicase proteins is one of the key steps in the replication process of all RNA viruses. However, the mechanisms underlying this phenomenon, including primary RNA elements that are recognized by the viral replicase proteins, are not well understood. Here, we used aptamer pulldown assays with membrane fractionation and protein-RNA coimmunoprecipitation in a cell-free viral translation/replication system to investigate how viral replicase proteins recognize the bipartite genomic RNAs of the Red clover necrotic mosaic virus (RCNMV). RCNMV replicase proteins bound specifically to a Y-shaped RNA element (YRE) located in the 3' untranslated region (UTR) of RNA2, which also interacted with the 480-kDa replicase complexes that contain viral and host proteins. The replicase-YRE interaction recruited RNA2 to the membrane fraction. Conversely, RNA1 fragments failed to interact with the replicase proteins supplied in trans. The results of protein-RNA coimmunoprecipitation assays suggest that RNA1 interacts with the replicase proteins coupled with their translation. Thus, the initial template recognition mechanisms employed by the replicase differ between RCNMV bipartite genomic RNAs and RNA elements are primary determinants of the differential replication mechanism.
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Affiliation(s)
- Hiro-oki Iwakawa
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Akira Mine
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Kiwamu Hyodo
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Mengnan An
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Masanori Kaido
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Kazuyuki Mise
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Tetsuro Okuno
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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97
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Mine A, Hyodo K, Takeda A, Kaido M, Mise K, Okuno T. Interactions between p27 and p88 replicase proteins of Red clover necrotic mosaic virus play an essential role in viral RNA replication and suppression of RNA silencing via the 480-kDa viral replicase complex assembly. Virology 2010; 407:213-24. [PMID: 20828775 DOI: 10.1016/j.virol.2010.07.038] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2010] [Revised: 07/13/2010] [Accepted: 07/23/2010] [Indexed: 11/16/2022]
Abstract
Red clover necrotic mosaic virus (RCNMV), a positive-sense RNA virus with a bipartite genome, encodes p27 and p88 replicase proteins that are required for viral RNA replication and suppression of RNA silencing. In this study, we identified domains in p27 and p88 responsible for their protein-protein interactions using in vitro pull-down assays with the purified recombinant proteins. Coimmunoprecipitation analysis in combination with blue-native polyacrylamide gel electrophoresis using mutated p27 proteins showed that both p27-p27 and p27-p88 interactions are essential for the formation of the 480-kDa complex, which has RCNMV-specific RNA-dependent RNA polymerase activity. Furthermore, we found a good correlation between the accumulated levels of the 480-kDa complex and replication levels and the suppression of RNA silencing activity. Our results indicate that interactions between RCNMV replicase proteins play an essential role in viral RNA replication and in suppressing RNA silencing via the 480-kDa replicase complex assembly.
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Affiliation(s)
- Akira Mine
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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98
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Stork J, Kovalev N, Sasvari Z, Nagy PD. RNA chaperone activity of the tombusviral p33 replication protein facilitates initiation of RNA synthesis by the viral RdRp in vitro. Virology 2010; 409:338-47. [PMID: 21071052 PMCID: PMC7173327 DOI: 10.1016/j.virol.2010.10.015] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2010] [Revised: 09/19/2010] [Accepted: 10/12/2010] [Indexed: 12/18/2022]
Abstract
Small plus-stranded RNA viruses do not code for RNA helicases that would facilitate the proper folding of viral RNAs during replication. Instead, these viruses might use RNA chaperones as shown here for the essential p33 replication protein of Tomato bushy stunt virus (TBSV). In vitro experiments demonstrate that the purified recombinant p33 promotes strand separation of a DNA/RNA duplex. In addition, p33 renders dsRNA templates sensitive to single-strand specific S1 nuclease, suggesting that p33 can destabilize highly structured RNAs. We also demonstrate that the RNA chaperone activity of p33 facilitates self-cleavage by a ribozyme in vitro. In addition, purified p33 facilitates in vitro RNA synthesis on double-stranded (ds)RNA templates up to 5-fold by a viral RNA-dependent RNA polymerase. We propose that the RNA chaperone activity of p33 facilitates the initiation of plus-strand synthesis as well as affects RNA recombination. Altogether, the TBSV RNA chaperone might perform similar biological functions to the helicases of other RNA viruses with much larger coding capacity.
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Affiliation(s)
- Jozsef Stork
- Department of Plant Pathology, University of Kentucky, Lexington, KY 40546, USA
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99
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Li Z, Pogany J, Tupman S, Esposito AM, Kinzy TG, Nagy PD. Translation elongation factor 1A facilitates the assembly of the tombusvirus replicase and stimulates minus-strand synthesis. PLoS Pathog 2010; 6:e1001175. [PMID: 21079685 PMCID: PMC2973826 DOI: 10.1371/journal.ppat.1001175] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Accepted: 10/01/2010] [Indexed: 11/18/2022] Open
Abstract
Replication of plus-strand RNA viruses depends on host factors that are recruited into viral replicase complexes. Previous studies showed that eukaryotic translation elongation factor (eEF1A) is one of the resident host proteins in the highly purified tombusvirus replicase complex. Using a random library of eEF1A mutants, we identified one mutant that decreased and three mutants that increased Tomato bushy stunt virus (TBSV) replication in a yeast model host. Additional in vitro assays with whole cell extracts prepared from yeast strains expressing the eEF1A mutants demonstrated several functions for eEF1A in TBSV replication: facilitating the recruitment of the viral RNA template into the replicase complex; the assembly of the viral replicase complex; and enhancement of the minus-strand synthesis by promoting the initiation step. These roles for eEF1A are separate from its canonical role in host and viral protein translation, emphasizing critical functions for this abundant cellular protein during TBSV replication. Plus-stranded RNA viruses are important pathogens of plants, animals and humans. They replicate in the infected cells by assembling viral replicase complexes consisting of viral- and host-coded proteins. In this paper, we show that the eukaryotic translation elongation factor (eEF1A), which is one of the resident host proteins in the highly purified tombusvirus replicase complex, is important for Tomato bushy stunt virus (TBSV) replication in a yeast model host. Based on a random library of eEF1A mutants, we identified eEF1A mutants that either decreased or increased TBSV replication. In vitro studies revealed that eEF1A facilitated the recruitment of the viral RNA template for replication and the assembly of the viral replicase complex, as well as eEF1A enhanced viral RNA synthesis in vitro. Altogether, this study demonstrates that eEF1A has several functions during TBSV replication.
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Affiliation(s)
- Zhenghe Li
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Judit Pogany
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Steven Tupman
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Anthony M. Esposito
- Department of Molecular Genetics, Microbiology, and Immunology, UMDNJ Robert Wood Johnson Medical School, Piscataway, New Jersey, United States of America
| | - Terri Goss Kinzy
- Department of Molecular Genetics, Microbiology, and Immunology, UMDNJ Robert Wood Johnson Medical School, Piscataway, New Jersey, United States of America
| | - Peter D. Nagy
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky, United States of America
- * E-mail:
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100
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Martínez-Turiño S, Hernández C. Identification and characterization of RNA-binding activity in the ORF1-encoded replicase protein of Pelargonium flower break virus. J Gen Virol 2010; 91:3075-84. [PMID: 20826617 DOI: 10.1099/vir.0.023093-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
Abstract
Pelargonium flower break virus (PFBV) belongs to the genus Carmovirus (family Tombusviridae) and, as with the remaining members of the group, possesses a monopartite genome of single-stranded, positive-sense RNA that contains five ORFs. The two 5'-proximal ORFs (ORFs 1 and 2) encode two polypeptides of 27 and 86 kDa (p27 and p86), respectively, that show homology with replication proteins. The p27 does not present any motif to explain its presumed involvement in replication, while p86 has the motifs conserved in RNA-dependent RNA polymerases. In this work, we have confirmed the necessity of p27 and p86 for PFBV replication. To gain insights into the function(s) of p27, we have expressed and purified the protein from Escherichia coli and tested its ability to bind RNA in vitro. The results have shown that p27 is able to bind ssRNA with high affinity and in a cooperative fashion and that it is also capable of binding other types of nucleic acids, though to a lesser extent. Additionally, competition experiments suggest that p27 has a preference for PFBV-derived ssRNAs. Using truncated forms of p27, it can be concluded that several regions of the protein contribute to its RNA-binding properties and that this contribution is additive. This study is the first to show nucleic acid-binding ability of the ORF1 product of a carmovirus and the data obtained suggest that this product plays an essential role in selection and recruitment of viral RNA replication templates.
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Affiliation(s)
- Sandra Martínez-Turiño
- Instituto de Biología Molecular y Celular de Plantas (Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia), Ciudad Politécnica de la Innovación, Ed. 8E, Camino de Vera s/n, 46022 Valencia, Spain
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